Modified clay paper coating

ABSTRACT

A modified clay paper coating composition comprising a montmorillonite clay having at least partially hydrolyzed aluminum chloride bonded thereto is made by treating montmorillonite clay with a non-aqueous solution of anhydrous aluminum chloride following by hydrolyzing with hot water. A paper substrate coated with this composition exhibits improved image light fastness when employed in a pressure-sensitive duplication system.

BACKGROUND OF THE INVENTION

This invention relates to a clay coating composition for use inpressure-sensitive duplication systems and the method for making thiscomposition. The invention further relates to a modified clay-coatedsheet for use in pressure-sensitive duplication systems.

The pressure-sensitive duplication systems of the prior art aregenerally based on the color-forming reaction between anelectron-donating colorless compound and an electron-accepting solidsubstance. Examples of this type of system are described in U.S. Pat No.2,712,507 of Green and U.S. Pat. No. 2,730,456 of Green, et al.

In the prior art duplication systems, a number of ways to facilitate thecontact of the color-forming reactants have been devised. These systemsinclude (1) a combination of an upper sheet having on its lower surfacea layer of microcapsules containing an electron-donating colorlesscompound (referred to as a color-developing substance) and a lower sheethaving on its upper surface a layer of an electron-accepting solidmaterial (referred to as a color-forming substance); (2) a three-sheetcombination wherein the intermediate sheet is coated on one surface withthe color-developing substance and on the other surface with thecolor-forming substance; and (3) a single sheet being coated on the samesurface with both the color-forming and color-developing substances.

Illustrative of the electron-donating colorless compounds used ascolor-developing substances in pressure-sensitive duplication systemsare malachite green lactone, benzoyl leuco methylene blue, crystalviolet lactone, 3-methyl-2, 2'spirobi (benzol [f] chromene),3-dialkylamino-7-dialkylamino-flourans, alkyl- or aryl- substitutedspiro-dinaphthopyrans and alkyl-or aryl-substituted spiro-dibenzopyrans.Electron-accepting solid substances suitable for use inpressure-sensitive duplication systems as a colorforming substanceinclude active clay, acid clay, bentonite, kaolin, talc, aluminumsilicate, aluminum citrate, zinc oxide, titanium oxide, aluminum oxide,arsenic oxide, zinc chloride, aluminum chloride, stannous or stannicchloride, and antimony chloride (see, for example, U.S. Pat. No.3,442,908 of Orita, et. al.).

Clay compositions are also used generally in the paper industry asfillers and coating compositions for ordinary paper stock. Rowland, U.S.Pat. No. 2,307,239, discloses such a general purpose clay compositionwhich is made by forming a dry mixture of kaolin and a metal salt suchas sodium chloride, potassium chloride, aluminum chloride, etc.,followed by heating in the range of 785° to 965° C. for between one andfive hours.

While the pressure-sensitive duplication systems of the prior artgenerally exhibit good image formation, the prior art has failed toprovide a system which will remain colorfast upon extended exposure tolight.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a pressure-sensitiveduplication sheet which exhibits improved image light fastness whencompared with the prior art duplication sheets.

It is a further object of this invention to provide a modifiedmontmorillonite clay coating composition containing hydrolyzed aluminumchloride which results in improved image light fastness inpressure-sensitive duplication systems.

In accordance with this invention there is provided a modified claypaper coating composition for use in pressure-sensitive duplicationsystems comprising a montmorillonite clay having at least partiallyhydrolyzed aluminum chloride bonded thereto. The invention furtherprovides for a method of making this composition which comprisestreating montmorillonite clay with a non-aqueous solution of anhydrousaluminum chloride to bond the aluminum chloride to the clay and then atleast partially hydrolyzing the bonded aluminum chloride. The inventionalso embraces a modified clay coated sheet for use in pressure-sensitiveduplication systems comprising a paper substrate coated with the abovedescribed composition, and an improved pressure-sensitive duplicationsystem employing this coated sheet.

DESCRIPTION OF THE INVENTION

The basic raw materials required for the practice of the presentinvention include clay, aluminum chloride, a nonaqueous solvent, andwater.

The clay material can be any of the "montmorillonite" type clays. Thepreferred clay is sodium bentonite, however, other montmorillonite clayssuch as those based on calcium or magnesium can be advantageouslyemployed. The clay material can also contain normal quantities ofnon-clay or non-montmorillonite impurities without adversely affectingthe objects of the present invention. The clay should, however, besubstantially dry, although minor amounts of residual moisture will notbe deleterious to the process. The clay material may be employed in anyform which can be easily suspended in a liquid to form a relativelyuniform dispersion.

The aluminum chloride employed in the practice of the present inventionshould be anhydrous aluminum chloride. Any suitable grade of anhydrousaluminum chloride may be used since the presence of minor amounts ofimpurities will not seriously affect the process of the presentinvention. This reagent is preferably employed in finely dividedpowdered form.

The non-aqueous solvent employed in the process of the present inventioncan be any non-aqueous liquid which meets the following requirements:

1. The solvent should be aprotic, i.e., one that does not readily giveup or accept protons; (2) it should have at least some solvent action onAlCl₃ ; (3) it should be otherwise both chemically and physicallynon-reactive towards AlCl₃ ; and (4) it should be either volatile orwater soluble. Carbon tetrachloride is the preferred example of thissolvent, however, other suitable solvents include chloroform, diethylether, benzene, nitrobenzene and the like.

According to the preferred process of this invention the montmorilloniteclay is first dried and then slurried with a non-aqueous solvent asdescribed above. Sufficient solvent is added to suspend all the claypresent. The amount of solvent employed in this step is not critical andit will be readily apparent to one of ordinary skill in the art how muchsolvent will produce a slurry of workable consistency. It may also bedesirable to employ an excess amount of solvent to form the initialsuspension and then distill off a portion of the solvent to achieve thedesired consistency. This optional distillation step will also removethe last traces of unbound water from the surface of the clay. Theslurrying step is preferably performed at room temperature, althoughelevated temperatures can be employed if desired.

The next step of the process of the present invention is the addition ofanhydrous aluminum chloride to the clay slurry described above. Thisresults in the bonding of the entire AlCl₃ molecule to the clay. Ingeneral the amount of AlCl₃ added can be from about 0.01 to about 1.0moles of AlCl₃ per 100 grams of clay, and preferably is from about 0.05to about 0.2 moles of AlCl₃ per 100 grams of clay. Greater amounts mayalso be used. If the capacity of the clay for bonding AlCl₃ is exceeded,the unreacted AlCl₃ can be removed in the later described washing step.In order to achieve uniform distribution of the AlCl₃ throughout theclay, it is desirable to agitate the mixture. The reaction which resultsin bonding of the AlCl₃ to the clay proceeds rapidly, but as theroutineer will appreciate, it may be necessary to allow suitable timefor intimate contact of the reactants. Generally contact times of fromabout thirty minutes to about ten hours can be employed. The AlCl₃addition can preferably take place at room temperature, although anysuitable temperature, for example, in the range of 50° to 100° C. may beemployed.

In the next step in the process of the present invention, the aboveproduced slurry is filtered and washed with a nonaqueous solvent, asdefined above. Preferably this solvent can be the same one used tooriginally suspend the clay. The amount of solvent used in the washingstep is not critical and is simply that amount necessary to insureadequate contact of the filtered clay solids with the washing solvent.The washing step may be carried out at room temperature or, if desired,at slightly elevated temperature.

The treated and washed clay solids containing bonded AlCl₃ are nextredispersed in water to form an aqueous slurry. Determination of theamount of water required for this redispersion is well within the skillof the art, as any amount which will form a slurry of workableconsistency may be employed. This slurrying step is preferably performedat room temperature although elevated temperatures may be employed ifdesired.

The aqueous slurry formed in the preceding step is next subjected to amild heat treatment to promote the hydrolysis of the bonded AlCl₃. Thisheat treatment can be in the range of about 30° C. to about 100° C. Inthe preferred embodiment the aqueous slurry is warmed over a steam bath.This heating step should generally be continued for a period of fromabout one to about six hours, however, both the time and the temperaturemay be varied to achieve the desired amount of hydrolysis. At least 30%,and preferably between 60% and 95%, of the bonded AlCl₃ is hydrolyzedduring this step.

In the final step of the process of the present invention, the treatedclay solids are recovered from the aqueous slurry by vacuum filteringand drying. The resulting product is a montmorillonite clay having atleast partially hydrolyzed aluminum chloride bonded thereto.

The modified montmorillonite clay composition may be coated byconventional methods onto a paper substrate to form the coatedpressure-sensitive duplication sheet of the present invention. Whencontacted with a conventional color-developing substance, the modifiedclay coated sheets of the present invention form an image which exhibitsgreatly improved fade resistance upon exposure to light. The objects ofthis invention can be achieved by employing any of the well knowncolor-developing substances normally used in conjunction with clay orother electron-accepting substances. Examples of such color-developingsubstances include malachite green lactone, benzoyl leuco methyleneblue, crystal violet lactone, rhodamine B lactam, 3-methyl-2, 2'-spirobi(benzol [f] chromene), 3-dialkylamino-7-dialkylamino-flourans, alkyl- oraryl-substituted spiro-dinaphthopyrans and alkyl- or aryl-substitutedspiro-dibenzopyrans.

The following examples are included for illustrative purposes only andare not intended to limit the scope of the invention.

EXAMPLE 1

Sodium bentonite (50 grams-E clay dried three hours at 100°-110° C.under vacuum) was slurried with 250 milliliters carbon tetrachloride and75 milliliters solvent was distilled from the mixture. After the mixturehad cooled, 6.65 grams (0.05 mole) of aluminum chloride were added withstirring and the mixture was allowed to stand overnight. After stirringone additional hour at room temperature the mixture was filtered andwashed with 100 milliliters dry carbon tetrachloride. Evaporation of asmall portion of the carbon tetrachloride filtrate yielded only a traceof residue, indicating that the aluminum chloride remained with thebentonite. The treated clay was then slurried with 500 milliliters ofwater and warmed on a steam bath for about six hours. The material wasthen vacuum filtered and dried.

EXAMPLE 2

A sample of the modified clay coating composition prepared according toExample 1 is applied as a coating to a paper substrate by conventionalcoating techniques, and fade-resistance tests are performed byincorporating this coated sheet into a standard pressure-sensitiveduplication system employing benzoyl leuco methylene blue as acolor-developing substance. The image that is formed on the coated paperof the present invention does not reach 50% fade (MacBeth yellow filter)in nearly triple the exposure time taken by the unmodified clay coatingsof the prior art.

We claim:
 1. A modified clay composition for use in pressure-sensitiveduplication systems, said composition comprising montmorillonite clayhaving aluminum chloride bonded thereto, at least 30% of said aluminumchloride being hydrolyzed, whereby the image formed by reacting saidcomposition with a color-developing substance has increased faderesistance upon exposure to light.
 2. The composition of claim 1 whereinsaid montmorillonite clay is sodium bentonite.
 3. A process for making amodified clay composition for use in pressure-sensitive duplicationsystems, said process comprising treating a montmorillonite clay with anon-aqueous solution of anhydrous aluminum chloride to bond saidaluminum chloride to said clay, and hydrolyzing at least 30% of thebonded aluminum chloride, whereby the image formed by reacting saidcomposition with a color-developing substance has increased faderesistance upon exposure to light.
 4. The process of claim 3 whereinsaid montmorillonite clay is sodium bentonite.
 5. A process for making amodified clay for use in pressure-sensitive duplication systems, saidprocess comprisingdispersing a montmorillonite clay in a non-aqueoussolvent to form a first slurry, treating said first slurry withanhydrous aluminum chloride to bond said aluminum chloride to said clay,recovering the aluminum chloride-treated montmorillonite clay solidsfrom said first slurry, redispersing the aluminum-chloride treatedmontmorillonite clay solids in water to form a second slurry, heatingsaid second slurry to a temperature of about 30° C. to about 100° C., tohydrolyze at least 30% of the aluminum chloride, and recovering thepartially hydrolyzed aluminum chloride-containing montmorillonite clayfrom said second slurry.
 6. A process according to claim 5 wherein saidmontmorillonite clay is sodium bentonite.
 7. The process of claim 5wherein said non-aqueous solvent is selected from the group consistingof carbon tetrachloride, chloroform, diethyl ether, benzene andnitrobenzene.